Methods and systems for detecting cab signals

ABSTRACT

A method is provided for distinguishing a valid locomotive control signal from an invalid control signal resulting from the presence of at least one interfering signal. The method includes detecting a signal, and transforming the signal into the frequency domain to create a transformed signal having a number of frequency domain peaks. The validity of the signal is determined based on at least of a number, a spacing, and a magnitude of the frequency domain peaks in the transformed signal.

BACKGROUND OF THE INVENTION

This invention relates generally to control systems used with railroad systems, and more specifically, to methods and systems for distinguishing cab signals from noise.

Known railroads establish at least some speed limits in certain sections of track via cab signals. These signals are comprised of; for example, low-frequency carriers that are keyed off and on at various low data rates. The carriers are transmitted as currents through the rails. The currents are detected by magnetic pickup coils mounted on the underside of the locomotive, and a cab signal receiver installed in the locomotive is used to demodulate the cab signal and measure the on-off keying rate. The measured rate represents the speed limit for that particular section of track. The cab signal informs the operator/control the speed limit/actions to be followed. When the cab signal receiver detects that the locomotive has exceeded the determined speed limit an alarm is sounded to enable the locomotive engineer to take appropriate action. In some installations, the cab signal receiver may halt the train if the engineer fails to respond within a pre-determined period of time.

Modern locomotives use alternating current, AC, traction motors that are built into the axles of the locomotive drive wheels. Varying the frequency of the applied AC drive voltage controls the speed of the motor. Since the motors are positioned in close proximity to the cab signal receiver pickup coils, the variable AC signal may interfere with the received cab signal, which may result in the possibility of an incorrect speed limit detection. For example, a 57 Hz electromagnetic interference (EMI) from a traction motor may mix with a 60 Hz ambient EMI to create an in-band carrier (between 57 and 63 Hz) having a modulation rate of 3 Hz or 180 ppm code rate, which may create interference with a 60 Hz cab signal. Such interference may cause the cab signal receiver to indicate an erroneous speed limit than that established by the signal transmitted in the rails.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a method is provided for distinguishing a valid locomotive control signal from an invalid control signal resulting from the presence of at least one interfering signal. The method includes detecting a signal, and transforming the signal into the frequency domain to create a transformed signal having a number of frequency domain peaks. The validity of the signal is determined based on at least of a number, a spacing, and a magnitude of the frequency domain peaks in the transformed signal.

In another embodiment, a cab signal system for a locomotive is provided. The system includes at least one inductive pickup coil assembly configured to receive and transmit a signal and a cab signal receiver electrically coupled to the at least one inductive pickup coil assembly. The receiver is configured to detect a signal, and transform the signal into the frequency domain to create a transformed signal having a number of frequency domain peaks. The validity of the signal is determined based on at least of a number, a spacing, and a magnitude of the frequency domain peaks in the transformed signal.

In yet another embodiment, a cab signal receiver is provided. The receiver is configured to detect a signal, and transform the signal into the frequency domain to create a transformed signal having a number of frequency domain peaks. The validity of the signal is determined based on at least of a number, a spacing, and a magnitude of the frequency domain peaks in the transformed signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of an exemplary cab signal pickup coil assembly that may be mounted to the underside of a locomotive;

FIG. 2 is a schematic illustration of an exemplary pickup coil used with the coil assembly shown in FIG. 1 to generate an output signal;

FIG. 3 is a flowchart of an exemplary method for transforming the output signal generated by the pickup coil shown in FIG. 2; and

FIG. 4 is a graphical comparison of exemplary output signals generated using the method illustrated in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an algorithm for measuring and rejecting electromagnetic interference (EMI) when detecting a cab signal. Specifically, when two EMI sources are mixed, generally only two frequency domain peaks appear equivalent to the two mixing frequencies. However, when a carrier is modulated by a square wave, such as occurs in a true cab signal, at least three frequency domain peaks are created. Using this difference an algorithm can be used to detect valid cab signals and reject a cab signal created by mixing two EMI sources. An algorithm using this difference can also distinguish a valid cab signal from an invalid cab signal created by mixing a valid or invalid cab signal with one or more EMI sources.

FIG. 1 is a schematic block diagram of an exemplary pair of cab signal pickup coil assemblies 100 that may be mounted to the underside of a locomotive (not shown). In the exemplary embodiment, each cab signal pickup coil assembly 100 includes a U-shaped core 102 that includes a first leg pickup coil assembly 104, a second leg pickup coil assembly 106, and a connecting bar 108 that extends between leg 104 and leg 106. One or more magnetic pickup coils 110 are substantially concentrically arranged about each pickup coil assembly 104 and 106. A cab signal receiver 112 installed in the locomotive is electronically coupled to each pickup coil assembly 100. An alternating magnetic field 114 circulates about a rail 116 that is near cab signal pickup coil assembly 100. The magnetic field 114 is channeled through U-shaped core 102 and interacts with pickup coils 110 that generate an output signal that is relative to the strength and frequency of the magnetic field 14. Although FIG. 1 illustrates a magnetic field 114 circulating about only the left rail 116, as will be appreciated by one of ordinary skill in the art, a magnetic field 114 may also circulate about the right rail 116 or may circulate about both the left and right rail 116.

The magnetic field 114 is induced by current flow through rail 116. The field 114 interacts with pickup coils 110 that generate an output signal. Cab signal receiver 112 demodulates the output signal and measures the on-off keying rate of the signal. In the exemplary embodiment, the measured keying rate represents a speed limit for the locomotive. In other embodiments, the measured rate may be representative of any other signal or command associated with controlling the locomotive.

FIG. 2 schematically illustrates pickup coil 110 generating an output signal 150 that is representative of a command for controlling operation of the locomotive. Specifically in FIG. 2, the magnetic field 114 and electromagnetic interference are comingled as coil 110 generates output signal 150. In the exemplary embodiment, pickup coil 110 interacts with a magnetic field from three sources. In particular, in the exemplary embodiment, pickup coil 110 interacts with a 60 Hz magnetic field 114 induced about rail 116, a 60 Hz ambient electromagnetic interference 154, and a 57 Hz electromagnetic interference 156 generated by an AC traction motor 158 installed on the locomotive. In an alternative embodiment, interference 156 has a frequency of 63 Hz. Further, as will be appreciated by one of ordinary skill in the art, the magnetic fields described herein may have any frequency that results in interference similar to the interference described herein.

In the exemplary embodiment, during normal operations, pickup coil 110 interacts with magnetic field 114 and generates a 60 Hz output signal 150 that pulses at 3 Hz. In the exemplary embodiment, commands for controlling the operation of the locomotive are predetermined to include a 60 Hz signal pulsing at 3 Hz. Accordingly, interaction with magnetic field 114 would communicate a command for the locomotive. However, interaction with interference 154 and/or interference 156 may also cause pickup coil 110 to generate a 60 Hz output signal 150 that pulses at 3 Hz. Accordingly, such interaction, with interference 154 and interference 156, may cause pickup coil 110 to indicate an erroneous command to the locomotive.

FIG. 3 is a flowchart 200 of an exemplary method 202 for transforming coil output signal 150. Specifically, in the exemplary embodiment, the method 202 is used to separate or distinguish an output signal, generated by magnetic field 114, from an output signal, generated by a combination of interference 154 and interference 156. FIG. 4 is a graphical comparison of the output signals through each step of method 202, as described in more detail below.

In the exemplary embodiment, the method 202 includes detecting 210 an output signal 150 using cab signal receiver 112 and inputting the signal 150 into receiver 112. In one embodiment, output signal 150 is filtered 216 to form a filtered signal 218. In one embodiment, signal 150 is filtered with a bandpass filter. More specifically, as shown in FIG. 4, the output signal generated by magnetic field 114 is filtered to form signal 220, and the output signal generated by the combination of interference 154 and interference 156 is filtered to form signal 222. In the exemplary embodiment, signal 220 includes a plurality of pulses 224 that indicate a command for operating the locomotive. However, as illustrated in FIG. 4, signal 222 also includes a plurality of pulses 226 that are similar to pulses 224. Accordingly, as discussed above, signal 222 may erroneously indicate a command for controlling the locomotive.

As such, method 202 also includes rectifying 228 the filtered signal 218 to generate a rectified signal 230. In the exemplary embodiment, signal 220 is rectified to create a signal 232 and, similarly, signal 222 is rectified to create a signal 234. Signal 232, in the exemplary embodiment, includes a plurality of pulses 236 and, similarly, signal 234 includes a plurality of pulses 238. Accordingly, after rectifying 218 the signals 220 and 222, substantial similarities between signals 232 and 234 may still enable signal 234 to erroneously indicate a command for controlling the locomotive.

Accordingly, the method 202 also includes averaging 240 the rectified signal 230 to generate an averaged signal 242. Specifically, in the exemplary embodiment, rectified signal 232 is averaged to create signal 244, and rectified signal 234 is averaged to create signal 246. In the exemplary embodiment, signal 244 includes a plurality of steps 248 and, similarly, signal 246 includes a plurality of steps 250. Accordingly, after averaging 240 signals 232 and 234, the resultant signals 244 and 246 are still substantially similar enough that signal 246 may erroneously indicate a command for controlling the locomotive.

The method 202 also includes parallel processing by transforming 252 either signal 150, 218, 230, or 242 into the frequency domain to generate a transformed signal 254. Specifically, in the exemplary embodiment, signal 150, 218, 230, or 242 is transformed into the frequency domain using at least one of a Fast Fourier Transform and a Discrete Fourier Transform. More specifically, in the exemplary embodiment, signal 220, 232, or 244 is transformed to create signal 256, and signal 222, 234, or 246 is transformed to create signal 258. Signal 256 includes a center frequency domain peak 260 and at least two side frequency domain peaks 262 and 264. Specifically, when a carrier is modulated by a square wave, such as a true cab signal, at least three frequency domain peaks are created. In the exemplary embodiment, side frequency domain peaks 262 and 264 are created on both sides of center frequency domain peak 260. In an alternative embodiment, side frequency domain peaks 262 and 264 may be created on only one of either side of center frequency domain peak 260. Further, in the exemplary embodiment, signal 258 includes a center frequency domain peak 266 and one side frequency domain peak 268. Specifically when two EMI sources are mixed, only two frequency domain peaks appear approximately equivalent to the two mixing frequencies. In the exemplary embodiment, side frequency domain peak 268 is created on the left side of center frequency domain peak 266. However, as will be appreciated by one of ordinary skill in the art, side frequency domain peak 268 may be created on the right side of center frequency domain peak 264.

Accordingly, in one embodiment, the signal 220 generated by magnetic field 114 can be distinguished from the signal 222 generated by a combination of interference 154 and interference 156, based on the number of side frequency domain peaks that are present in the transformed signal 220 or 222. Specifically, the method 202 includes determining 270 the validity of the signal by counting the number of side frequency domain peaks in the transformed signal. More specifically, a signal is determined to be a cab signal based its transformed signal including two side frequency domain peaks on at least one side of a center frequency domain peak, as illustrated by transformed signal 256. Further, a signal is determined to be a noise signal based on its transformed signal including one side frequency domain peak, as is illustrated in transformed signal 258. In the exemplary embodiment, the step of counting the side frequency domain peaks is automatically performed using cab signal receiver 112. In an alternative embodiment, the step of counting the side frequency domain peaks is manually performed by an engineer.

Further, in another embodiment, determining 270 the validity of the signal can be based upon a relative magnitude and a spacing of the frequency domain peaks. Specifically, with regard to using magnitude, the smaller of the two side bands, when both signal and noise are present, represents the signal. Accordingly, the relative amplitude of the lower and upper side bands can be used to determine 270 whether the signal is a valid cab signal or an invalid signal resulting from interference.

Moreover, in one embodiment, the on and off times of the averaged signals 244 and 246 are determined. Accordingly, the output signal 150 is passed if it is a valid cab signal.

In one embodiment, the method 202 also includes determining the frequencies of center frequency domain peak 260 and side frequency domain peaks 262 and 264, and transforming 252 future averaged signals based on the determined frequencies. Accordingly, the step of transforming 252 can be customized to the frequencies of signal 220 to facilitate improving the detection of cab signals. Moreover, in one embodiment, the method 202 also includes continually detecting a signal determined to be a cab signal, and filtering out other signals and/or noise. Accordingly, the step of detecting 210 a signal can be improved to facilitate detecting only cab signals.

The present invention facilitates improving cab signal detection in the presence of noise. Specifically, noise or EMI from traction motors near the carrier frequency of 60 Hz and ambient EMI of 60 Hz can combine or mix together and emulate a coded 60 Hz cab signal rate. For example, 57 Hz EMI from the traction motors may mix with 60 Hz ambient EMI to create an in band carrier (between 57 and 63 Hz) with a modulation rate of 3 Hz or 180 ppm code rate. The present invention measures and rejects this mixing phenomenon. Specifically when two EMI sources are mixed, only two frequency domain peaks appear approximately equivalent to the two mixing frequencies. Further, when a carrier is modulated by a square wave, such as a true cab signal, at least three frequency domain peaks are created. Specifically, two side frequency domain peaks are created on at least one side of a center frequency domain peak. Accordingly, the number of frequency domain peaks in a transformed signal can be counted to determine whether a signal is a valid cab signal or an invalid signal created by mixing two EMI sources. Accordingly, the present invention facilitates improving reliability in distinguishing between true cab signals and emulated cab signals due to EMI. Specifically, the present invention facilitates improving cab signal operation in high EMI environments, reducing costs associated with cab signal operation, and improving cab signal operation in dark territories.

As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

In one embodiment, a method is provided for distinguishing a valid locomotive control signal from an invalid control signal resulting from the presence of at least one interfering signal. The method includes detecting a signal, and transforming the signal into the frequency domain to create a transformed signal having a number of frequency domain peaks. The validity of the signal is determined based on at least of a number, a spacing, and a magnitude of the frequency domain peaks in the transformed signal. In one embodiment, transforming the signal includes transforming the signal using at least one of a Fast Fourier Transform and a Discrete Fourier Transform. Further, in one embodiment, the method includes detecting a signal determined to be a valid signal, and filtering out at least one of other signals and noise.

In one embodiment, the method includes determining that the signal is valid based on the transformed signal including a center frequency domain peak at an expected frequency and an upper and lower side band on each side of the center frequency domain peak. In such an embodiment, a minimum of the upper and lower side bands is used to acquire information regarding the signal. Further In such an embodiment, a second signal is transformable based on the center frequency domain peak and a frequency of each of the upper and lower side bands. In another embodiment, the method includes determining that the signal is invalid based on the transformed signal including a center frequency domain peak and a single side band on at least one side of the center frequency domain peak.

Exemplary embodiments of systems and methods for distinguishing a cab signal from noise are described above in detail. The systems and methods illustrated are not limited to the specific embodiments described herein, but rather, components of the system may be utilized independently and separately from other components described herein. Further, steps described in the method may be utilized independently and separately from other steps described herein.

While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims. 

1. A method for distinguishing a valid locomotive control signal from an invalid control signal resulting from the presence of at least one interfering signal, said method comprising: detecting a signal; transforming the signal into the frequency domain to create a transformed signal having a number of frequency domain peaks; and determining the validity of the signal based on at least one of a number, a spacing, and a magnitude of the frequency domain peaks in the transformed signal.
 2. A method in accordance with claim 1 wherein determining the validity of the signal further comprises determining that the signal is valid based on the transformed signal including a center frequency domain peak at an expected frequency and an upper and lower side band on each side of the center frequency domain peak.
 3. A methods method in accordance with claim 2 further comprising using a minimum of the upper and lower side bands to acquire information regarding the signal.
 4. A method in accordance with claim 2 further comprising transforming a second signal based on the center frequency domain peak and a frequency of each of the upper and lower side bands.
 5. A method in accordance with claim 1 wherein determining the validity of the signal further comprises determining that the signal is invalid based on the transformed signal including a center frequency domain peak and a single side band on at one side of the center frequency domain peak.
 6. A method in accordance with claim 1 wherein transforming the signal further comprises transforming the signal using at least one of a Fast Fourier transform and a Discrete Fourier Transform.
 7. A method in accordance with claim 1 further comprising: detecting a signal determined to be a valid signal; and filtering out at least one of other signals and noise.
 8. A cab signal system for a locomotive, said system comprising: at least one inductive pickup coil assembly configured to receive and transmit a signal; and a signal receiver electrically coupled to said at least one inductive pickup coil assembly, said receiver configured to: detect a signal; transform the signal into the frequency domain to create a transformed signal having a number of frequency domain peaks; and determine the validity of the signal based on at least one of a number, a spacing, and a magnitude of the frequency domain peaks in the transformed signal.
 9. A system in accordance with claim 8 wherein said receiver is configured to determine that the signal is valid based on the transformed signal including a center frequency domain peak at an expected frequency and an upper and lower side band on each side of the center frequency domain peak.
 10. A system in accordance with claim 9 wherein said receiver is further configured to use a minimum of the upper and lower side bands to acquire information regarding the signal.
 11. A system in accordance with claim 9 wherein said receiver is configured to transform a second signal based on the center frequency domain peak and a frequency of each of the upper and lower side bands.
 12. A system in accordance with claim 8 wherein said receiver is further configured to determine that the signal is invalid based on the transformed signal including a center frequency domain peak and a single side band on at least one side of the center frequency domain peak.
 13. A system in accordance with claim 8 wherein said receiver is further configured to transform the signal using at least one of a Fast Fourier Transform and a Discrete Fourier Transform.
 14. A system in accordance with claim 8 wherein said receiver is further configured to: detect a signal determined to be a valid signal; and filter out at least one of other signals and noise.
 15. A cab signal receiver configured to: detect a signal; transform the signal into the frequency domain to create a transformed signal having a number of frequency domain peaks; and determine the validity of the signal based on at least one of a number, a spacing, and a magnitude of the frequency domain peaks in the transformed signal.
 16. A cab signal receiver in accordance with claim 15 configured to determine that the signal is valid based on the transformed signal including a center frequency domain peak at an expected frequency and an upper and lower side band on each side of the center frequency domain peak.
 17. A cab signal receiver in accordance with claim 16 further configured to use a minimum of the upper and lower side bands to acquire information regarding the signal.
 18. A cab signal receiver in accordance with claim 16 configured to transform a second signal based on the center frequency domain peak and a frequency of each of the upper and lower side bands.
 19. A cab signal receiver in accordance with claim 15 further configured to determine that the signal is invalid based on the transformed signal including a center frequency domain peak and a single side band on at least one side of the center frequency domain peak.
 20. A cab signal receiver in accordance with claim 15 further configured to transform the signal using at least one of a Fast Fourier Transform and a Discrete Fourier Transform. 